[PATCH V2] xfs: do not allow reflinking inodes with the dax flag set

[Eric Sandeen <sandeen@redhat.com>]

Today, xfs_reflink_remap_prep() will reject inodes which are in the CPU
direct access state, i.e. IS_DAX() is true.  However, it is possible to
have inodes with the XFS_DIFLAG2_DAX set, but which are not activated as
dax, due to the flag being set after the inode was loaded.

To avoid confusion and make the lack of dax+reflink crystal clear for the
user, reject reflink requests for both IS_DAX and XFS_DIFLAG2_DAX inodes
unless DAX mode is impossible due to mounting with -o dax=never.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---
V2: Allow reflinking dax-flagged inodes in "mount -o dax=never" mode

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 6fa05fb78189..e238a5b7b722 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -1308,6 +1308,15 @@ xfs_reflink_remap_prep(
 	if (IS_DAX(inode_in) || IS_DAX(inode_out))
 		goto out_unlock;
 
+	/*
+	 * Until we have dax+reflink, don't allow reflinking dax-flagged
+	 * inodes unless we are in dax=never mode.
+	 */
+	if (!(mp->m_flags & XFS_MOUNT_DAX_NEVER) &&
+	     (src->i_d.di_flags2 & XFS_DIFLAG2_DAX ||
+	      dest->i_d.di_flags2 & XFS_DIFLAG2_DAX))
+		goto out_unlock;
+
 	ret = generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
 			len, remap_flags);
 	if (ret || *len == 0)